U.S. patent application number 10/882423 was filed with the patent office on 2006-01-05 for chemical-mechanical post-etch removal of photoresist in polymer memory fabrication.
Invention is credited to Ebrahim Andideh, Richard M. Steger.
Application Number | 20060000493 10/882423 |
Document ID | / |
Family ID | 35512658 |
Filed Date | 2006-01-05 |
United States Patent
Application |
20060000493 |
Kind Code |
A1 |
Steger; Richard M. ; et
al. |
January 5, 2006 |
Chemical-mechanical post-etch removal of photoresist in polymer
memory fabrication
Abstract
An embodiment of the invention is a method of removing
photoresist. More specifically, an embodiment is a method of
removing photoresist utilized to pattern the top electrode metal
layer in a polymer memory device substantially without damaging the
underlying polymer or top electrode metal by utilizing a high
pressure photoresist solvent spray.
Inventors: |
Steger; Richard M.;
(Beaverton, OR) ; Andideh; Ebrahim; (Portland,
OR) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD
SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Family ID: |
35512658 |
Appl. No.: |
10/882423 |
Filed: |
June 30, 2004 |
Current U.S.
Class: |
134/33 ; 134/34;
257/E21.244; 257/E21.255; 257/E21.663 |
Current CPC
Class: |
B08B 3/02 20130101; H01L
21/6708 20130101; H01L 27/1159 20130101; G03F 7/422 20130101; H01L
21/31053 20130101; H01L 21/31133 20130101 |
Class at
Publication: |
134/033 ;
134/034 |
International
Class: |
B08B 7/00 20060101
B08B007/00 |
Claims
1. A method comprising: spraying a solvent on a substrate with a
high pressure spray wherein the substrate includes a layer of
photoresist and exposed ferroelectric polymer of a polymer
ferroelectric memory device.
2. The method of claim 1 further comprising: spraying the solvent
on the substrate with a low pressure spray.
3. The method of claim 1 further comprising: rotating the wafer
during the high pressure spraying.
4. The method of claim 3, rotating the wafer further comprising:
rotating the wafer approximately between 25 and 1500 revolutions
per minute.
5. The method of claim 4, rotating the wafer further comprising:
rotating the wafer at approximately 50 revolutions per minute.
6. The method of claim 1 wherein the solvent has a temperature
approximately between 20.degree. C. and 90.degree. C.
7. The method of claim 6 wherein the solvent has a temperature of
approximately 70.degree. C.
8. The method of claim 1 wherein the solvent has a pressure of
approximately between 100 and 500 pounds per square inch.
9. The method of claim 8 wherein the solvent has a pressure of
approximately 400 pounds per square inch.
10. The method of claim 1 wherein the high pressure spray has a
duration of approximately between 10 and 1000 seconds.
11. The method of claim 10 wherein the high pressure spray has a
duration of approximately 300 seconds.
12. The method of claim 1 wherein the solvent is selected from the
group consisting of a glycol ether based solvent, ASHLAND EZSTRIP
100, ARCH MS5010, and SHIPLEY XP-0215.
13. The method of claim 1 wherein the photoresist comprises T.O.K.
601B photoresist.
14. The method of claim 1 wherein the high pressure spray is
substantially cone-shaped.
15. The method of claim 1 wherein the high pressure spray is
substantially fan-shaped.
16. The method of claim 1 further comprising: pivoting a high
pressure spray nozzle across the surface of the wafer to
substantially completely expose the surface of the wafer to the
high pressure spray.
17. A method comprising: spraying a solvent on a substrate with a
first low pressure spray wherein the substrate includes a layer of
photoresist and exposed ferroelectric polymer of a polymer
ferroelectric memory device; spraying the solvent on the substrate
with a high pressure spray after the first low pressure spray.
18. The method of claim 17 further comprising: spraying the solvent
on the substrate with a second low pressure spray after the high
pressure spray.
19. The method of claim 18 further comprising rotating the wafer
during the first low pressure spray, the high pressure spray, and
the second low pressure spray.
20. The method of claim 19, rotating the wafer further comprising
rotating the wafer approximately between 25 and 1500 revolutions
per minute during the first low pressure spray.
21. The method of claim 20, rotating the wafer further comprising
rotating the wafer at approximately 50 revolutions per minute
during the first low pressure spray.
22. The method of claim 19, rotating the wafer further comprising
rotating the wafer approximately between 25 and 1500 revolutions
per minute during the high pressure spray.
23. The method of claim 22, rotating the wafer further comprising
rotating the wafer at approximately 50 revolutions per minute
during the high pressure spray.
24. The method of claim 19, rotating the wafer further comprising
rotating the wafer approximately between 25 and 1500 revolutions
per minute during the second low pressure spray.
25. The method of claim 24, rotating the wafer further comprising
rotating the wafer at approximately 50 revolutions per minute
during the second low pressure spray.
26. The method of claim 19 wherein one of the first low pressure
spray, high pressure spray, and second low pressure has a rotation
direction different than another of the first low pressure spray,
high pressure spray, and second low pressure spray.
27. The method of claim 18 wherein the solvent has a temperature
approximately between 20.degree. C. and 90.degree. C.
28. The method of claim 27 wherein the solvent has a temperature of
approximately 70.degree. C.
29. The method of claim 18 wherein the solvent has a pressure of
approximately between 10 and 100 pounds per square inch for the
first low pressure spray.
30. The method of claim 29 wherein the solvent has a pressure of
approximately 90 pounds per square inch for the first low pressure
spray.
31. The method of claim 18 wherein the solvent has a pressure of
approximately between 100 and 500 pounds per square inch for the
high pressure spray.
32. The method of claim 31 wherein the solvent has a pressure of
approximately 400 pounds per square inch for the high pressure
spray.
33. The method of claim 18 wherein the solvent has a pressure of
approximately between 10 and 100 pounds per square inch for the
second low pressure spray.
34. The method of claim 33 wherein the solvent has a pressure of
approximately 90 pounds per square inch for the second low pressure
spray.
35. The method of claim 18 wherein the first low pressure spray has
a duration of approximately between 10 and 200 seconds.
36. The method of claim 35 wherein the first low pressure spray has
a duration of approximately 90 seconds.
37. The method of claim 18 wherein the high pressure spray has a
duration of approximately between 10 and 1000 seconds.
38. The method of claim 37 wherein the high pressure spray has a
duration of approximately 300 seconds.
39. The method of claim 18 wherein the second low pressure spray
has a duration of approximately between 10 and 200 seconds.
40. The method of claim 35 wherein the second low pressure spray
has a duration of approximately 90 seconds.
41. The method of claim 18 wherein the solvent is selected from the
group consisting of a glycol ether based solvent, ASHLAND EZSTRIP
100, ARCH MS5010, and SHIPLEY XP-0215.
42. The method of claim 18 wherein the photoresist comprises T.O.K.
601B photoresist.
43. The method of claim 18 wherein the high pressure spray is
substantially cone-shaped.
44. The method of claim 18 wherein the high pressure spray is
substantially fan-shaped.
45. The method of claim 18 further comprising pivoting a high
pressure spray nozzle across the surface of the wafer to
substantially completely expose the surface of the wafer to the
high pressure spray.
46. A method comprising: removing a photoresist layer from a
substrate including an exposed ferroelectric polymer and an exposed
metal, each of a polymer ferroelectric memory device, with a high
pressure solvent spray wherein the exposed ferroelectric polymer
and the exposed metal are substantially undamaged by the high
pressure solvent spray.
47. The method of claim 46 wherein the ferroelectric polymer
comprises polyvinylidene fluoride.
48. The method of claim 46 wherein the ferroelectric polymer
comprises a copolymer of polyvinylidene fluoride and
trifluoroethylene.
49. The method of claim 46 wherein the solvent comprises a glycol
ether based solvent.
50. The method of claim 46 wherein the pressure of the high
pressure solvent spray is approximately between 100 and 500 pounds
per square inch.
51. The method of claim 50 wherein the pressure of the high
pressure solvent spray is approximately 400 pounds per square inch.
Description
FIELD
[0001] Embodiments of the invention relate to semiconductor
processing techniques, and specifically to photoresist removal
techniques.
BACKGROUND
[0002] Memory manufacturers are currently researching and
developing the next generation of memory devices. One such
development includes technology designed to replace current Flash
non-volatile memory technology. Important elements of a Flash
successor include compactness, low price, low voltage operation,
non-volatility, high density, fast read and write cycles, and long
life.
[0003] Current Flash technology is predicted to survive into 90
nanometer and 65 nanometer process generations. This survival is in
part based on, for example, exotic storage dielectric material,
cobalt and nickel source and drain regions, copper and low
dielectric constant materials for the interconnect levels, and high
dielectric constant materials for transistor gate dielectrics.
However, there will thereafter exist a need for new memory
materials and technology, particularly for non-volatile memory.
[0004] Ferroelectric memory is one such technology aimed to replace
Flash memory. A ferroelectric memory device combines the
non-volatility of Flash memory with improved read and write speeds.
Simply stated, ferroelectric memory devices rely on the use of
ferroelectric materials that can be spontaneously polarized by an
applied voltage or electric field and that maintain the
polarization after the voltage or field has been removed. As such,
a ferroelectric memory device can be programmed with a binary "1"
or "0" depending on the orientation of the polarization. The state
of the memory device can then be detected during a read cycle.
[0005] Two crystalline materials have emerged as promising films
utilized in a ferroelectric memory scheme, namely lead zirconium
titanate ("PZT") and strontium bismuth tantalite ("SBT"). However,
while the materials exhibit appropriate ferromagnetic properties,
each is nevertheless expensive to integrate into an existing CMOS
process.
[0006] More recent developments include the use of polymers that
exhibit ferroelectric properties. The creation of polymer
ferroelectric memory utilizes polymer chains with net dipole
moments. Data is stored by changing the polarization of the polymer
chain between metal lines that sandwich the layer comprised of the
ferroelectric polymer chain. Further, the layers can be stacked
(e.g., metal word line, ferroelectric polymer, metal bit line,
ferroelectric polymer, metal word line, etc.) to improve memory
element density. The polymer ferroelectric memory devices exhibit
microsecond initial read speeds coupled with write speeds
comparable to Flash.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1: illustration of a ferroelectric beta phase
polyvinylidene fluoride (PVDF) molecule chain
[0008] FIG. 2: illustration of a top view of a polymer
ferroelectric memory device
[0009] FIG. 3: illustration of a substrate cross section of a
polymer ferroelectric memory device after the top electrode metal
has been blanket deposited
[0010] FIG. 4: illustration of a substrate cross section of a
polymer ferroelectric memory device after the photoresist has been
deposited and patterned
[0011] FIG. 5: illustration of a substrate cross section of a
polymer ferroelectric memory device after the top electrode metal
has been etched
[0012] FIG. 6: illustration of a substrate cross section of a
polymer ferroelectric memory device after the photoresist removal
process of an embodiment
[0013] FIG. 7: illustration of a photoresist removal tool and the
nitrogen purge of an embodiment
[0014] FIG. 8: illustration of a photoresist removal tool an the
low pressure chemical spray of an embodiment
[0015] FIG. 9: illustration of a photoresist removal tool and the
high pressure chemical spray of an embodiment
[0016] FIG. 10: illustration of a high pressure chemical spray arm
motion of an embodiment
[0017] FIG. 11: illustration of a high pressure chemical spray arm
motion of an embodiment with a cone-shaped spray
[0018] FIG. 12: illustration of a high pressure chemical spray arm
motion of an embodiment with a fan-shaped spray
[0019] FIG. 13: illustration of a photoresist removal tool and
another low pressure spray of an embodiment
DETAILED DESCRIPTION
[0020] Embodiments of a method of removing photoresist are
described. Reference will now be made in detail to a description of
these embodiments as illustrated in the drawings. While the
embodiments will be described in connection with these drawings,
there is no intent to limit them to drawings disclosed herein. On
the contrary, the intent is to cover all alternatives,
modifications, and equivalents within the spirit and scope of the
described embodiments as defined by the accompanying claims.
[0021] Simply stated, an embodiment of the invention is a method of
removing photoresist. More specifically, an embodiment is a method
of removing photoresist utilized to pattern the top electrode metal
layer in a polymer memory device substantially without damaging the
underlying polymer by utilizing a low pressure photoresist solvent
spray, a high pressure photoresist solvent spray, and/or a
combination thereof.
[0022] As noted, a large portion of the historical research in
ferroelectric memory device technology has centered on select
crystalline materials such as PZT and SBT. More current trends,
however, include utilizing polymer chains that exhibit
ferroelectric properties. Polyvinylidene Fluoride ("PVDF") is a
fluoropolymer with alternating CH.sub.2 and CF.sub.2 groups for
which the relative electron densities between the hydrogen and
fluorine atoms create a net ionic dipole moment. FIG. 1 illustrates
the ferroelectric beta phase PVDF 100, including a chain of carbon
110 and alternating and opposing hydrogen 120 and fluorine 130
pairs. A particular PVDF copolymer is polyvinylidene fluoride
trifluoroethylene ("PVDF-TrFE"). The addition of the
trifluoroethylene C.sub.2HF.sub.3 (essentially substituting a
hydrogen with a fluorine) in the chain reduces the overall
theoretical ionic dipole moment of a ferroelectric PVDF beta phase
chain, but increases the likelihood of forming the ferroelectric
PVDF beta phase versus the paraelectric PVDF alpha phase during
crystallization. The crystalline PVDF-TrFE polymer is ferroelectric
in that it can be given a remanent polarization that can be
switched in a sufficiently high electric field (i.e., a coercive
field). The polarization can be used to store a binary "0" state
and a binary "1" state of a memory device fabricated therewith
based on the orientation of the polarization.
[0023] Memory elements utilizing polymer ferroelectric materials
can be passive in the sense that there is no need for active
components (e.g., a transistor coupled to a MOS capacitor in DRAM).
Data is stored by changing the polarization of the polymer chain
between metal lines that sandwich the layer comprised of the
ferroelectric polymer. The elements are driven externally by
applying a voltage to the appropriate word and bit lines to read or
write to a polymer ferroelectric memory cell. Configured as such,
the read cycle is destructive and the memory cell must be rewritten
akin to a DRAM refresh cycle.
[0024] FIG. 2 illustrates a top view of a single layer polymer
ferromagnetic memory device. Bit lines 250-280 and word lines
210-240 sandwich a layer of polymer ferroelectric material 200.
When a voltage is applied across overlapping bit and word lines
(e.g., bit line 250 and word line 240) a number of operational
processes are possible. A relatively high voltage (e.g., ranging
approximately between 8 and 10 volts), can create a coercive
electric field sufficient to program a binary "1" state or a binary
"0" state based on altering the orientation of the remanent
polarization of the polymer ferroelectric material 200 sandwiched
between the bit and word lines 250 and 240 respectively. A separate
voltage can be applied, in conjunction with external detection
circuitry not illustrated, to read the binary state of the memory
cell.
[0025] There are a variety of processing challenges associated with
fabricating polymer ferroelectric memory devices. One challenge is
to deposit and pattern materials adjacent to the ferroelectric
polymer layer as the ferroelectric polymer is susceptible to damage
by certain processing steps common to, for example, photoresist
removal. Further, the photoresist removal that is compatible with
the ferroelectric polymer must simultaneously not damage (e.g., by
etching) exposed metal.
[0026] As is well known in the art, photoresist is a photosensitive
organic polymer utilized in the photolithographic process. Once the
photoresist has been used to pattern for example an etch,
deposition, or implant process step as is well known in the art, it
is removed and the exposed substrate is cleaned in preparation for
subsequent process steps. Photoresist removal (also called
photoresist strip, or PR strip) can occur by a variety of different
mechanisms and combinations thereof. For example, the photoresist
may be removed with a solvent, and may further be subject to sonic
energy while being exposed to the solvent. The photoresist may also
be removed by ashing whereby the substrate is exposed to an
oxygen-containing plasma that thermally decomposes the photoresist.
The ashing may be followed by a solvent or rinse process step to
remove any remaining photoresist or photoresist ash.
[0027] FIGS. 3 through 6 depict substrate cross sections to
illustrate metal layer patterning processing steps associated with
a metal electrode of a polymer memory device. A substrate 300 onto
which the polymer ferroelectric memory is fabricated can be any
substrate onto which it would be useful to fabricate a memory
device, ranging from, for example, a bulk silicon wafer to the top
interconnect, dielectric, or passivation layer of a dual damascene
process architecture. Metal 310 is the bottom electrode of the
polymer memory and forms, for example, one of word lines 210-240
word line illustrated by FIG. 2. Metal 310 can be any metal
suitable as electrode material in a polymer memory device. For
example, metal 310 may be titanium, titanium oxide, titanium
nitride, aluminum, tantalum, gold, silver, tungsten, ruthenium,
rhodium, palladium, platinum, cobalt, nickel, iron, copper, or
alloys thereof. A polymer layer 320 is deposited atop the metal 310
layer. In an embodiment, the polymer layer 320 is polyvinylidene
fluoride. In another embodiment, the polymer layer 320 is a
copolymer of polyvinylidene fluoride and trifluoroethylene. The
addition of the trifluoroethylene reduces the overall theoretical
electrical dipole of the PVDF molecule chain, but increases the
likelihood that the PVDF molecule will orient in its ferroelectric
beta phase. Metal 330 is the basis for the top electrode of the
polymer memory that will form, for example and following the
processes of FIGS. 4 through 6, bit lines 250-280. Metal 330 can be
any metal suitable as electrode material in a polymer memory
device. For example, metal 330 may be titanium, titanium oxide,
titanium nitride, aluminum, tantalum, gold, silver, tungsten,
ruthenium, rhodium, palladium, platinum, cobalt, nickel, iron,
copper, or alloys thereof.
[0028] FIG. 4 illustrates the substrate 300 of FIG. 3 following the
deposition and patterning of photoresist layer 400. Though not
illustrated, photoresist layer 400 is, for example, spin-coat
deposited as a blanket layer on top of the metal 330 blanket layer
to be patterned. Using well known photolithographic techniques, the
photoresist is patterned to expose select areas of the metal 330
layer.
[0029] FIG. 5 illustrates the substrate 300 of FIG. 4 following the
removal of select portions of the metal 330 layer to fabricate, for
example, bit lines 250-280. As introduced, metal 330 may be
titanium, titanium oxide, titanium nitride, aluminum, tantalum,
gold, silver, tungsten, ruthenium, rhodium, palladium, platinum,
cobalt, nickel, iron, copper, or alloys thereof. In an embodiment,
the metal is removed with a reactive ion etch with BCl.sub.3,
Cl.sub.2, argon, helium, or combinations thereof. After portions of
the metal 330 layer have been removed, portions of the polymer
layer 320 are exposed.
[0030] FIG. 6 illustrates the substrate 300 of FIG. 5 following the
removal of photoresist layer 400. As noted, there are a variety of
methods common to photoresist removal including ashing and/or
solvent strip as introduced above. However, traditional methods of
photoresist removal are not fully compatible with the polymer layer
320. For example, given that the photoresist and polymer layer are
organic polymers, solvents useful to remove photoresist may also
damage the polymer layer. Similarly, ashing the photoresist with an
oxygen-containing plasma may also cause damage to the polymer
layer. A method of an embodiment removes photoresist 400 in the
presence of exposed ferroelectric polymer 320 substantially without
damaging the ferroelectric polymer 320 and substantially without
damaging metal 330 by adding mechanical energy to a wet photoresist
removal chemistry. During the photoresist 400 removal, the polymer
320 is not exposed to oxygen-containing plasma that may damage the
polymer 320.
[0031] FIG. 7 illustrates a cross section of a photoresist removal
tool 700. Inside a chamber 770, the photoresist removal tool
includes a fixture 720 to hold a wafer 710 in place during the
photoresist removal process. As used herein, wafer 710 includes or
is the substrate on which the polymer memory is fabricated. In an
embodiment, the wafer 710 is oriented such that the face of the
wafer 710 (i.e., the side of the wafer including the fabricated
circuit elements) is facing down and toward the source of a solvent
spray that is sprayed up toward the wafer 710 surface. Further, in
an embodiment, the fixture 720 is configured to spin the wafer
710.
[0032] Once the wafer 710 is secure in the fixture 720, the ambient
within the chamber 770 is purged with, for example, nitrogen to
evacuate substantially all of the oxygen in the chamber. In an
embodiment, and as will be discussed more fully below, the wet
photoresist removal chemistry may include, for example, metal
corrosion inhibitors that degrade if oxidized. The nitrogen purge
reduces that oxidizing exposure.
[0033] Once the chamber 770 is purged with, for example, nitrogen,
the low pressure chemical spray manifold 750, including a plurality
of low pressure nozzles 780, sprays the surface of the wafer 710
with a wet photoresist removal chemistry as illustrated by FIG. 8.
In an embodiment the wafer 710 is spinning in the fixture 720 to
aid uniformity in wet photoresist removal chemistry coverage. The
pressure of the wet photoresist removal chemistry is approximately
between 10 and 100 pounds per square inch. In an embodiment, the
wet photoresist removal chemistry pressure is approximately 90
pounds per square inch. The wet photoresist removal chemistry has a
temperature of approximately between 20.degree. C. and 90.degree.
C. In an embodiment, the wet photoresist removal chemistry
temperature is approximately 70.degree. C. The low pressure
chemical spray manifold 750 sprays the wafer 710 with the
aforementioned parameters for approximately between 10 and 200
seconds. In an embodiment the low pressure chemical spray manifold
750 sprays the wafer 710 for approximately 90 seconds. During the
spray, the wafer 710 may be spun in the fixture 720 at
approximately between 25 and 1500 revolutions per minute. In an
embodiment, the wafer is spun in the fixture 720 at approximately
50 revolutions per minute. During the low pressure spray of an
embodiment, a high pressure chemical spray arm 760 is withdrawn,
swung aside, or otherwise moved so as to not interfere with the
spray from the low pressure chemical spray manifold 750.
[0034] Generally speaking, the wet photoresist removal chemistry is
a glycol ether based solution that, among other constituents, may
contain water and a metal etch inhibitor so as to mitigate damage
to metal 330 during the photoresist 400 removal. In an embodiment,
photoresist 400 is T.O.K. 601B. In an embodiment, the wet
photoresist removal chemistry is ASHLAND EZSTRIP 100, ARCH MS5010,
or SHIPLEY XP-0215. Though an embodiment described herein utilizes
the same wet photoresist removal chemistry (i.e., solvent), it is
to be understood that each of the first low pressure, high
pressure, and second low pressure sprays may utilize different
solvents.
[0035] FIG. 9 illustrates the high pressure chemical spray of an
embodiment. After the wafer 710 has been sprayed by the low
pressure chemical spray manifold 750, the high pressure chemical
spray arm 760, including a high pressure nozzle 790, extends,
swings or otherwise positions underneath the wafer 710. The high
pressure nozzle then sprays the face of the wafer 710 with a wet
photoresist removal chemistry. The pressure of the wet photoresist
removal chemistry is approximately between 100 and 500 pounds per
square inch. In an embodiment, the wet photoresist removal
chemistry pressure is approximately 400 pounds per square inch. The
wet photoresist removal chemistry has a temperature of
approximately between 20.degree. C. and 90.degree. C. In an
embodiment, the wet photoresist removal chemistry temperature is
approximately 70.degree. C. The high pressure nozzle 790 sprays the
wafer 710 with the aforementioned parameters for approximately
between 10 and 1000 seconds. In an embodiment, the high pressure
nozzle 790 sprays the wafer 710 for 300 seconds. During the spray,
the wafer 710 may be spun in the fixture 720 at approximately
between 25 and 1500 revolutions per minute. In an embodiment, the
wafer is spun in the fixture 720 at approximately 50 revolutions
per minute.
[0036] FIG. 10 illustrates a bottom view of the wafer 710 and the
high pressure chemical spray arm 760 including the high pressure
nozzle 790. During the high pressure spray, the high pressure
chemical spray arm 760 is rotated about, for example, a pivot so
that the high pressure nozzle 790 sweeps an arc across the surface
of the wafer 710. In an embodiment, the wafer 710 is spinning in
the fixture 720 while the high pressure nozzle 790 is swept back
and forth in an arc across the surface of the wafer 710. The
combination of sweeping the high pressure nozzle 790 and spinning
the wafer 710 improves the uniformity with which the surface of the
wafer 710 is exposed to the wet photoresist removal chemistry.
[0037] The shape of the wet photoresist removal chemistry spray
emitting from the high pressure spray nozzle 790 can be altered to
adjust the coverage of the wafer. For example, the high pressure
spray nozzle 790 may spray the wet photoresist removal chemistry
substantially in a cone shape as illustrated by FIG. 11 and
cone-shaped spray 1100. The angle of the cone vertex may be altered
to control the shape of the cone. Further, the distance between the
high pressure spray nozzle 790 and the wafer 710 may be altered to
control the surface area covered by the spray for a given cone
vertex angle created by the high pressure spray nozzle 790.
[0038] FIG. 12 illustrates a fan-shaped spray 1200 of an
embodiment. The fan-shaped spray 1200 of an embodiment operates in
conjunction with the high pressure chemical spray arm 760 rotated
about, for example, a pivot so that the high pressure nozzle 790
sweeps an arc across the surface of the wafer 710 to uniformly
expose the surface of the wafer 710 to the wet photoresist removal
chemistry. As with the cone-shaped spray 1100, the vertex angle of
the fan-shaped spray 1200 and/or the distance between the wafer 710
and the high pressure spray nozzle 790 may be adjusted to control
the surface area covered by the fan-shaped spray 1200 of an
embodiment.
[0039] The effectiveness of the photoresist layer 400 removal
depends in significant part on the addition of mechanical energy to
the wet photoresist etch chemistry. As noted, adding sonic energy
has been one approach utilized to encourage the solvent removal of
photoresist. For example, the sonic energy may be in the form of
ultrasonic (i.e., greater than 20,000 hertz) vibration as the, for
example, wafer 710 including a photoresist layer 400 is submerged
in a photoresist solvent. However, it is difficult to apply sonic
energy uniformly to the substrate as it is difficult to tune or
focus the sonic energy evenly over the entire surface of the
substrate. Further, sonic energy is directional. The same sonic
energy directionality that promotes photoresist removal, however,
tends to also shear the underlying ferroelectric polymer. Further,
the entire substrate is exposed to the sonic energy, potentially
damaging otherwise interior layers.
[0040] The solvent spray or sprays of an embodiment, in addition to
exposing the photoresist layer 400 to a solvent, adds mechanical
energy to the solvent substantially perpendicularly to the surface
of wafer 710. The spray parameters (e.g., pressure, nozzle size and
configuration, solvent type, solvent temperature, and duration of
spray), in combination with the motion of both the wafer 710 and,
if applicable, the motion of the high pressure chemical spray arm
760 can be adjusted to substantially uniformly expose the surface
of the wafer 710 to the wet photoresist removal chemistry. Further,
the same parameters, or a subset thereof, can be adjusted to
increase or decrease the mechanical energy experienced by the
surface of the wafer 710 to remove the photoresist layer 400
substantially without damaging the underlying polymer layer
320.
[0041] Once the wafer 710 has been exposed to the high pressure
spray, the low pressure chemical spray manifold 750, including a
plurality of low pressure nozzles 780, sprays the surface of the
wafer 710 with the wet photoresist removal chemistry as illustrated
by FIG. 13. In an embodiment the wafer 710 is spinning in the
fixture 720 to aid uniformity in wet photoresist removal chemistry
coverage. The pressure of the wet photoresist removal chemistry is
approximately between 10 and 100 pounds per square inch. In an
embodiment, the wet photoresist removal chemistry pressure is
approximately 90 pounds per square inch. The wet photoresist
removal chemistry has a temperature of approximately between
20.degree. C. and 90.degree. C. In an embodiment, the wet
photoresist removal chemistry temperature is approximately
70.degree. C. The low pressure chemical spray manifold 750 sprays
the wafer 710 with the aforementioned parameters for approximately
between 10 and 200 seconds. In an embodiment the low pressure
chemical spray manifold 750 sprays the wafer 710 for approximately
90 seconds. During the spray, the wafer 710 may be spun in the
fixture 720 at approximately between 25 and 1500 revolutions per
minute. In an embodiment, the wafer is spun in the fixture 720 at
approximately 50 revolutions per minute. During the low pressure
spray of an embodiment, a high pressure chemical spray arm 760 is
withdrawn, swung aside, or otherwise moved so as to not interfere
with the spray from the low pressure chemical spray manifold 750.
The second low pressure spray substantially removes any remaining
photoresist 400 from the wafer 710. In an embodiment, the second
low pressure spray may be omitted as substantially all of the
photoresist 400 is removed by the first low pressure spray and the
high pressure spray.
[0042] Following photoresist 400 removal, the wafer 710 may be
rinsed with, for example, deionized water to remove the wet
photoresist removal chemistry from the surface of the wafer 710. In
an embodiment, the deionized water rinse is preceded by a rinse
with ethylene glycol to prevent a reactive solvent from interacting
with the water to the extent that the solvent, for example,
precipitates solute or leaves a residue on the wafer 710 surface.
The wafer 710 may further be spun dry. In an embodiment, the wafer
710 is spun for approximately 180 seconds at approximately 1500
revolutions per minute. In an embodiment, the rinse and spin-dry is
performed by photoresist removal tool 700 so as to avoid
transferring or transporting a wet wafer. During the spin-dry, the
chamber 770 may be opened to the ambient atmosphere (i.e., dry air)
to facilitate drying.
[0043] As noted, the resulting rinsed and dried wafer 710 has had
the photoresist 400 removed in the presence of exposed
ferroelectric polymer 320. An embodiment removes the photoresist
400 without substantially damaging the ferroelectric polymer 320 as
the ferroelectric polymer 320 is neither exposed to a damaging
solvent nor exposed to an oxygen-containing plasma during the
photoresist 400 removal. Further, the metal 330 has not been
substantially damaged by exposure to the solvent. In an embodiment,
the result is a substantially intact layer of ferroelectric polymer
320 combined with a substantially intact layer of metal 330 that
has been patterned to form, for example, bit lines 250-280.
[0044] It is to be understood that the wafer may be spun in the
fixture either clockwise or counter clockwise relative to a
reference direction. For example, in an embodiment the wafer is
spun in one direction for the first low pressure spray and the high
pressure spray and in the other direction for the second low
pressure spray. However, the spin orientation may be altered
differently. Altering the spin direction may aid the uniformity
with which the wet photoresist removal chemistry removes
photoresist 400. For example, it may be that spinning the wafer 710
in the same direction for all sprays creates a leeward side to the
photoresist 400 topology and non-uniform photoresist 400
removal.
[0045] One skilled in the art will recognize the elegance of the
disclosed embodiment in that it mitigates one of the limiting
factors of fabricating polymer ferroelectric memory devices. By
avoiding ashing (i.e. exposure to oxygen-containing plasma)
photoresist removal steps, an embodiment substantially avoids
damaging the ferroelectric polymer during photolithographic
patterning steps during which the ferroelectric polymer is
exposed.
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